Frequency responsive control circuit



Feb. 14, 1950 c. K. GIERINGER ETAL 2,497,404

FREQUENCY RESPONSIVE CONTROL CIRCUIT Filed Feb. 5, 1947 3 Sheets-Sheet 1 I Feb. 14, 1950 c. K. GIERINGER ETAL 2,497,404

FREQUENCY RESPONSIVE CONTROL CIRCUIT Filed Feb. 5, 1947 3 Sheets-Sheet 2 DROP our vALuE awe/Mimi ZZW 6% WM, Mun

' @bbowws Feb. 14, 1950 c. K. GIVERINGER ETAL 2,497,404

FREQUENCY RESPONSIVE CONTROL CIRCUIT l at'en tecl Feb. 14, 1950 FREQUENCY RESPONSIVE CONTROL CIRCUIT Carl K. Gieringer and Arthur G. Billin, Cincinnati, Ohio, assignors to The Licbel-Flarsheim Company, Cincinnati, Ohio, a corporation of Ohio Application February 5, 1947, Serial No. 726,472

16 Claims. 1

This invention relates to oscillator circuits of the type employed in diathermy machines, high frequency heaters and various other devices which are used for medicinal, industrial and other purposes. The primary objective of the invention has been to provide apparatus capable of operating within a predetermined narrow frequency band in order that the operation of the apparatus will not interfere with communication channels at other frequencies assigned by the Federal Communications Commission. More specifically, the invention contemplates a short wave generator which is capable of operating with minimum variation from an assigned or predetermined frequency, independently of any misoperation by a doctor, nurse, or technician. The invention is disclosed particularly in relation to a diathermy machine circuit and, as described herein, performs within a variation of plus or minus onethird of one percent, but the apparatus is suitable for other purposes and for operation within even narrower limits of frequency variation.

A conventional short wave oscillator varies in frequency according to the impedance of the load connected to the machine, and according to the coupling of the generator with the output circuit. Under fixed load impedance conditions of operation and with proper care and attention, the conventional, well-designed oscillator has sufficient frequency stability to stay within a prescribed wave band. However, if a machine is misoperated, if the load impedance changes suddenly, or if the machine is not adjusted properly with respect to its load, then a frequency shift or variation will occur which will be more or less severe according to the extent of the improper coupling and mistuning. For instance, in a diathermy machine, should the controls be set for a high resistance patient circuit condition, and then should the operator inadvertently place the electrodes near each other in such a way as to approach resonance in the circuit, the frequency will deviate well beyond the present limits set by the Federal Communications Commision.

It is the purpose of the device of the present invention to render an oscillator incapable of continuing to operate should frequency variations of such magnitude tend to occur, or to monitor the oscillator for the purpose of confining its operation to a prescribed frequency band. The invention also contemplates a circuit in which a bell, buzzer or other suitable signal device is energized whenever the machine is decommissioned or departs from assigned frequency in order that the operator may be warned to readjust the apparatus. In addition, a cooperative control device is contemplated which may be used in conjunction with the frequency controller apparatus to protect the tubes of the generator circuit against becoming overloaded or becoming damaged in consequence of improper output circuit loading.

The present invention, briefly, is predicated upon the fact that the voltage across a tuned circuit is maximum at resonance frequency thereof and drops off rapidly as the frequency deviates above or below the point of resonance. In accordance with the present invention, a radio frequency voltage from the oscillator is applied through a high impedance to a tuned circuit such that the voltage across the tuned circuit is maximum when the oscillator frequency and the resonant frequency of the tuned circuit are at a predetermined or assigned value. When the oscillator frequency deviates from this assigned or predetermined value, either by increase or decrease, the voltage across the tuned circuit will decrease at a rate depending upon the characteristics of the tuned circuit. However, the high frequency response of a simple resonant circuit coupled to an oscillator is of such a nature that the rate of change of voltage in the resonant circuit decreases rapidly as the frequency of the oscillator deviates from resonant circuit frequency. Near resonant frequency, the slope of the response curve is quite steep, but with further deviations in frequency, the curve is of much less slope and the resonant circuit therefore is much less selective. It is the purpose of the present invention to provide an arrangement whereby an overall or net effective response is obtained having a substantially uniform and selective characteristic, that is, to provide a circuit in which the net effective response is more sensitive than the response exhibited by a simple resonant circuit.

In the utilization of such governing factors, one suitable circuit adapted to be employed involves rectification of a part of the voltage across the tuned circuit for the purpose of causing current to flow through one winding of a differential control relay. This current also is caused to flow through resistance for the purpose of providing a bias voltage which is applied to the control grid of a triode tube. In the preferred embodiment, the plate of the triode tube is connected to the input from the oscillator, for a source of radio frequency plate voltage, and the plate current of the triode tube is caused to flow through the other winding of the differential relay, the magnitude of the plate current being governed by the bias on the grid of the triode tube. Thus, the circuit is so arranged that when the current of the tuned circuit is maximum, and, correspondingly when the grid bias voltage for the triode tube is maximum, the plate current of the triode tube is at a minimum value. Otherwise expressed, a typical frequency controller adapted to be used in the practice of the invention comprises a resonant circuit having a portion of its voltage rectified for energization of one of the coils of the differential relay while the second portion of the frequency control device includes a triode tube through which the second differential winding of the controller relay is energized, but energized only in accordance with the bias voltage which is proportional to the voltage of the tuned circuit. The windings of the differential relay are arranged to generate opposing fluxes, and the relay, wherein the currents of the two coils produce opposed magnetomotive forces, operates a control switch or other device when the difference between the currents in the first and second circuits of the frequency controller reaches a predetermined amount, independently of the actual values of the currents. Thus, variations in the current of the resonant circuit, which conform to the variations in the voltage of the oscillator, are utilized to produce variations in the grid bias of a triode tube by which magnetomotive forces generated in the differential relay are compounded to produce a sensitizing or selective effect which is unaffected by substantial voltage variations of the generator but is critically responsive to variations in the frequency thereof within a very narrow wave band.

In operation of the apparatus, when the frequency of the oscillator deviates from resonance, the current in the tuned circuit of the frequency controller will decrease, thereby producing less flux in the first coil of the differential relay. This decrease in current also is manifest in the bias resistor; hence, the triode tube is subject to less bias and therefore, more plate current is allowed to flow therein to produce an increased flux in the second coil of the differential relay. When the net effective flux in the differential relay reaches a predetermined value, or that is, when the difference between the currents in the first and second circuits of the frequency controller just described has reached a predetermined amount, the relay is actuated to operate a switch for decommissioning the oscillator circuit, or to actuate other suitable control devices. Such a result is obtained whether the frequency deviation is above or below normal frequency, since voltage of the resonant circuit is a maximum only at resonance.

From the foregoing brief description of the principles upon which the invention is predicated and from the following detailed description of the drawings in which a typical embodiment of the improvement is disclosed, those skilled in the art readily will comprehend various modifications to which the invention is susceptible.

In the drawings:

Figure l is a diagram of a circuit suitable for use, by way of example, in a diathermy machine adapted for medical treatment purposes.

Figure 2 is a chart illustrating the shift of currents in the respective windings of the differentialcontrol relay and the net effective results, in response to variations in frequency of the oscillator.

Figure 3 is a modified form of circuit embodying the principles disclosed herein and also in- 4 corporating a protective device for preventing damage to the tubes of the oscillator in event of miscoupling.

For the purposes of description, the oscillator portion of the circuit shown in Figure 1 is embraced in the solid lines, while the control apparatus is embraced within the dotted lines. In fact, the control circuit is of such nature that all elements of it, including the control relay and a signal device or the like, conveniently may be housed within a compact casing ready for connection to the oscillator circuit as by means of a plug and socket adapter.

The oscillator circuit with which the frequency controller of the present invention is adapted to be used may be of any conventional electron tube short wave type. The circuit shown comprises a power triode tube having filament l, a plate 2, and a grid 3. The plate 2 is in connection with a tank coil 4 and a tank circuit condenser 5 which are connected in parallel with one another, and a trimmer condenser 6 shunts the tank circuit condenser 5 for the purpose of enabling accurate adjustment or establishment of the precise frequency at which the oscillator is to operate. The trimmer condenser is utilized to provide compensation when tubes are changed, when the parts may be mechanically misaligned, or to correct the circuit for other variations which may tend to shift the no-load frequency of the generator during its life. The tank circuit is grounded as at 1 through a condenser 8.

An output coil 9, connected to output leads it and II, is adjustably coupled with the tank coil 4.

Grid 3 of the oscillator is in connection with the filament I through grid bias resistance i2, this portion of the circuit also including a coupling coil 43, and condensers M, [5 and I6, respectively, and this portion of the circuit being grounded as at ill.

The oscillator is energized from input leads l8 and I9 which are connected with the primary winding of an input transformer 20 having three secondary windings 2i, 22 and 23. Secondary winding 2| is in connection with the filament through the leads an and y as indicated. Secondary winding 22 is in connection with the tank circuit and the tube circ-uit through the lead B and B. Connection of the third output winding, 23, of the input transformer is described at a later point in the specification.

Control circuit The circuit of the frequency controller device comprises a resonant circuit consisting of an inductance 3B and a capacitance 3! connected in parallel with one another. This resonant circuit is excited from the oscillator through a coil 33 which is coupled to the coil l3 of the oscillator circuit, and through a condenser 34, these elements being interconnected through lead 35.

For the purposes of the present description, the tubes of the control circuit are shown as a pair of triode tubes A and B. In construction, for convenience, these may be consolidated as a unitary double-triode tube, such as tube type IJ6,

70 3A5 or other suitable unit; however, for the purposes of the present description, the tubes are treated as separate or individual units.

Tube A is employed essentially as a diode or rectifier, therefore the plate 36 of tube A is in 7 connection with its grid 31 through a lead 38, and

a part of the voltage across the resonant circuit comprising the inductance 3t and condenser 3! is impressed upon tube A through a lead 39.

Filament 40 of the A unit is in connection, through leads AI and 42, with a bias resistance 43 and the return circuit from this resistance to the coil includes one winding, 44, of a differential relay which is indicated generally at 45. A condenser 48 bypasses radio-frequency currents around the relay winding.

The portion of the frequency controller circuit just described constitutes a circuit in which the current will decrease whenever the frequency of the oscillator circuit is above or below resonant frequency. Tube B has its plate 41 connected through lead 48 to lead furnishing the input voltage from the oscillator. This circuit contains condenser 49 to prevent direct current from flowing in the coupling coil 38 through which the frequency controller is coupled to the oscillator.

The filament 50 .of tube B is connected through leads 5| and 52 to the filament iil of tube A, whereby both filaments may be energized conveniently from a common source. In the circuit shown in Figure l, the filaments M! and 50 are energized through the leads a and b which are respectively interconnected with the terminals a and b of the secondary winding 23 of the input transformer,

and the respective terminals of the filaments til and 50 are shunted bycondenser 53.

Grid 54 of tube B is in connection through lead 55 with a grid resistor 56 and thence with the negative terminal of the bias resistor 43 of the resonant circuit just described. A radio-frequency choke coil 51 is connected to the plate ll of tube B and one terminal of the second winding 58 of the differential relay 35, while the other terminal of the second relay winding 58 is in connection with a lead 59 to the filaments 4d and 59. Capacitor 60 is connected across the lead 59 and the first relay winding M to bypass radio-frequency current around the bias resistance and a capacitor 6| is shunted across the second relay winding 58. Lead 59 is grounded as at 62.

For control purposes, in the circuit shown in the drawings, diiferential relay t5 operates a control switch which is arranged to disrupt the circuit between the filament return and B connection of the oscillator when frequency variations exceed a predetermined value and also. under such circumstances, to energize a signal device which is indicated generally at It. Switch '65 comprises two stationary contacts 55 and 5i,

and an intermediate movable contact 58 which is under the magnetic influence of core 69 of the differential relay 45. The movable contact is attracted into engagement with the stationary contact 67 under predetermined flux conditions of core 69 and a spring H urges the movable contact 58 into engagement with stationary contact 66 when the total effective flux of the core 69 drops to a predetermined value.

The 3- connection of the oscillator is grounded as at H. Contact 68 is grounded as at 52 through a lead 13. Contact .5? is in connection with the filament winding 21 of the transformer through leads M and "I5. hus, when contacts El and 68 are in engagement with one another the filament return circuit of the oscillator is completed through lead 75 from the transformer, lead it, contacts El and 68, lead 13 to ground er and thence from ground I! to B and this circuit is opened to decommission the oscillator when the sides to such a point that the spring II is able to separate the contact 58 from contact El.

A short circuiting switch it, which may be of the instantaneous type, is employed to initially establish completion of the filament return circuit, or to reestablish the circuit independently of contacts 5! and 38 at any time after the circuit has been opened at this point through action of the differential relay. Switch 18 has its contacts respectively connected with lead i l and lead ll; therefore, when switch it is closed the filament return circuit is completed through the filament transformer tap it to switch 16, thence through a lead ll to the lead '53 and through the ground to B as previously described.

The signal device iii controlled by switch 65 is energized from the a and 1) terminals of transformer winding 23. For example, the unit shown in the drawings comprises a buzzer having one terminal of its winding connected to the b terminal of the transformer winding 23, while the other terminal of the buzzer winding is in connection through lead '39 to the stationary contact of the control switch 65. Upon engagement of contact 68 with contact 56, a circuit for energizing the buzzer is completed through leads l3 and it to the a terminal of transformer winding 23. In place of a buzzer, a bell, light or other suitable device may be employed.

The operation of the circuit disclosed in Figure l is described in more detail as follows: Under proper operating conditions, when the oscillator frequency and the tuned frequency of the resonant circuit of the frequency controller coincide, the current in triode A of the frequency controller is maximum and the current of the triode B is minimum or zero, since the bias of resistor is high. Therefore, the flux of winding 44 of the differential rela 55 is high and the counteractive flux of winding 58 of the differential relay is zero or negligible; hence, contact 68 will reside in engagement with contact 5?. However, when the frequency of the oscillator deviates from the prescribed value, the effects thereof are compounded at the differential relay. First, the deviation in frequency causes a decrease in the current of the resonant circuit, that is, the current in the diode or rectifier A is decreased and, the differential relay winding 4 in connection with this portion of the control circuit suffers a loss in iiux. This decrease in fiux is accompanied by a loss in grid bias of tube B since the bias resistance is a part of the diode circuit. Therefore, more plate current is allowed to flow in the triode tube B, resulting in an increase of counteractive flux in the differential relay winding Hence, as the diode current decreases, the triode current increases. When a predetermined differential exists between the two, the relay opens switch contacts 6'5 and E3 to disrupt the circuit between the filament and the B lead of the oscillator. t the same time, contact 68 engages contact fit to energize the signal device. When this condition occurs the operator may reset the machine by returning the oscillator circuit through adjustment of the coupling between coils l and fl and by closing switch it to reestablish circuit connection between the filament return and 3* of the oscillator. In the manufacture of the unit, for practical purposes, it is convenient mechanically to interconnect the switch it with the coupling coil adjusting means of the oscillator such that switch '16 is closed when the coupling coil is moved to zero or to some low l coupling Value, and opened automatically as the coupling coil adjustment is increased.

Instead of breaking the circuit of the oscillator as just described, the frequency controller apparatus may be arranged to decommission the oscillator by opening a circuit at another point.

Figure 2 illustrates diagrammatically the responses in the respective windings 44 and 58 of the differential relay 45 which may be obtained in a circuit of this type in terms of D. C. current which is proportional to R. F. voltage. Curve A indicates the variation in current or flux in winding 44 as produced from the diode or A section of the frequency controller tube. Curve B represents the response or counteractive flux in winding 58 of the differential relay A5 in relation to frequency variation. The net eifective flux exerted by the differential relay upon movable contact 68 is the difference between the values of curves A and B for a frequency variation of any particular value. Thus, the resultant magnetomotive force on the relay, effective in respect to contact 68, is represented as curve C. If the relay is set for dropout value as indicated by the dotted line on this chart, it will be apparent that the frequency controller is sufficiently sensitive to exert a controlling effect upon the oscillator whenever the frequency varies slightly more than one-quarter of one percent above or below assigned value.

It may be noted that the slope of curve A is representative of the sensitivity or selectivity of a simple resonant circuit while a suitable rate of change is obtained upon deviation of the frequency in the one-eighth of one percent to threeeighths of one percent range, still at greater frequency deviations the curve is too fiat to produce a response adapted to be used for some control purposes. However, by the compound effect which is provided through the counteractive flux, as represented by curve B, the net effective flux, that is, the difference between curves A and B through a substantial range of frequency variation, exhibits the desired selectivity inasmuch as the slope of the curve is almost uniformly steep.

A further advantage of the present invention resides in the fact that if there is an overall increase or decrease in the voltage in the resonant circuit, nevertheless the resultant magnetomotive force acting upon relay 05 through the frequency range will coincide substantially with curve C. For example, if an increase of, say, ten percent exists in the voltage of the resonant circuit, there will be a corresponding voltage increase in the B section of the tube; hence, curve A will be shifted upwardly by ten percent, curve B shifted downwardly by ten percent and curve C, the difference between the two, will remain substantially as shown in the chart. such changes in overall voltage do occur in the operation of the equipment through increase or decrease in line voltage or changes in oscillator tube characteristics, but such changes do not affect the frequency selectivity of the frequency controller.

Figure 3 shows a circuit embodying a frequency control of the type described in conjunction with a device for protecting the plate of the oscillator power tube in event of overload. The oscillator circuit shown in Figure 3 is similar to the oscillater circuit of Figure l, and comprises a power tube 90 having a plate 9!, a grid 92 and a filament 93. The grid is connected through a coil 96 to a resistance 95 which is grounded as at 96, and a condenser 95a, is connected across the resistance 95.

Plate SI of the power tube is connected to one terminal of a tank coil 9! having its opposite terminal connected to ground I00 through a condenser I III. A condenser 98 is connected across the tank coil and a trimmer condenser 99 also is associated with this portion of the circuit for the purpose previously described. A radio fre quency choke coil I02 has one of its terminals connected to the ground terminal of the tank coil 9'! while its other terminal is connected through lead I 02 to the 13+ terminal of transformer winding 05 of the input transformer. The primary winding of the input transformer is indicated at I86 and the B terminal of winding I05 is in connection through lead I07 to the ground 96.

Tank coil 97 of the tank circuit of the oscillator is adjustably coupled with an output coil I09 as previously described. This adjustment is effected through a control shaft H0 having a control knob III. Shaft IIO serves other switching facilities as described in a later point of the specification.

The filament 93 of the tube is energized from a filament winding II2 of the input transformer I06. These connections are conventional and need not be described.

The frequency controller shown in Figure 3, like the controller shown and described in Figure l, embodies a resonant circuit indicated generally at H3, including a condenser IM and a coil II5. This circuit is in connection through lead I IS with a coil II? coupled to the coil 94 of the oscillator grid circuit. Coil III is grounded as at H3 and lead H6 includes condensers H9 and I20.

The frequency controller may include a double triode tube I22 of the type previously described com-prising sections A and B. Plate I 23 of the A section is in connection with the grid I24 thereof through a lead I25 so as to operate as a rectifier, and is supplied with potential from the resonant circuit I I 3 through lead I 26 taken from coil H5. Filament I2! of the A tube is in connection through lead I28 with a biasing resistor I 29, the latter being connected in series with a winding I39 on the difierential control relay which is indicated generally at I3I. The other terminal of this relay Winding is connected through leads I32 and I33 to the resonant circuit II 3. Lead I32 is grounded through condenser I59.

In the B section of tube I22, plate element I33 is connected to the lead H6 at a point intermediate condensers H9 and I20, while the grid I34 is connected to a grid resistance I35 from which a lead I35 is taken to the negative terminal of the bias resistor I29. Lead I36 is grounded at I 3? through a condenser I38. The plate I33 of the tube 3 is in connection through leads H6 and I 39 with a radio frequency choke coil I 40 which in turn is connected to the second winding iii of the differential relay I 3| This winding has its opposite terminal connected to filament lead I 28v through the connection I 32 which is grounded as at I43, and generates a flux in opposition to the flux of winding I3I. The choke coil Hill is grounded at I44 through a condenser Hi5.

In the tube B the filament I 47 has one terminal thereof connected through lead I48 to the fila ment I21 of the A tube. Both filaments are energized through leads I 49 and I50 which are respectively interconnected with a winding I5I of the input transformer I06, and the filament leads M9 and I50 are cross-connected through a bypass condenser I52.

The difierential control relay I3I actuates a switch indicated generally at I55, comprising stationary contacts I56 and I51 and an intermediate movable contact I58 which is in connection with ground I1I.

A plate current overload relay I60 also is arranged to actuate the movable contact I58. This relay comprises a winding I6I having one of its terminals interconnected through lead 52 to filament return lead I63. The opposite terminal of the winding I6I is connected through lead I64 to stationary contact I56.

Movable contact I58 has a portion thereof I65 ofiset to a point adjacent the armature I6Iaof the plate overload relay I60 such that the movable contact I56 is responsive to both the differential relay I3I and the plate overload relay 160. The relays are so designed that the differential relay I 3| will hold the movable contact I58 in engagement with the stationary contact I56 under proper frequency conditions and the relay I60 will be ineffective, excepting in the event that plate current of excessive value flows in the filament return lead I63 of the oscillator. When this condition occurs, the armature I6Ia of overload relay I60 exerts a force on the movable contact I58 sufficient to overcome the flux from the diiferential relay I3I, whereby the movable contact I58 is separated from the contact I56 and the oscillator circuit is thus opened.

The other stationary contact I51 of the control switch I55 is engaged by the movable contact I 8 of this switch either when there is excessive frequency shift or excessive plate current and it controls energization of a buzzer or other suitable signal unit I65a. The circuit shown comprises a lead I66 extending from the stationary contact 851 to one terminal of a winding I61 of the buzzer or signal unit. The opposite terminal of this winding is connected through lead I58 to a resistor I69. The other end of the resistor I69 is connected through lead 149 to one side of the transformer winding I5I and the junction between the buzzer winding I61 and the resistor I69 is connected through a lead I68 to a contact I18 on a control switch I10. Thus, the complete circuit to the buzzer includes transformer winding 151, lead I49, resistance I69, the signal unit winding I61, lead I66, the switch contacts I51 and I58 to ground at HI, and thence to the other terminal of the transformer winding I5I through the ground connection I43 and lead I50.

The switching facilities of the machine comprise switch I10 and a second switch I15. Switch I controls energization of the input transformer I06 and switch I10 has two functions; it short circuits the buzzer winding during tube warm up so that the buzzer does not operate during the starting period, and it completes a circuit between the B and the filament return of the oscillator independently of the differential control relay. For diathermy machine purposes, these switches preferably comprise movable contacts which are coupled, for actuation in unison, with control rod IIO which also governs the coupling of the oscillator to the output circuit. By virtue of these facilities, only one knob III need be employed as a control for energizing the filaments, placing the oscillator into operation, and adjusting the coupling. The arrangement provides the utmost simplicity because the only other control element which is necessary is a power control which may be arranged in the output circuit connected to coil I09.

For input control, switch I15 has its movable contact I14 connected to one of the input terminals I13. The stationary element I16 is connected to one terminal of the primary winding I06 of the input transformer while the other terminal of the transformer winding is connected to the other input terminal I80. As the control knob is moved from zero to off position toward the on position, the movable contact I14 engages the stationary contact to energize the input transformer and maintains such engagement during further movement in the same direction of the control knob. The switching operation energizes the filament of the power tube of the oscillator through the winding H2 and also energizes the filaments of the A and B tubes of the frequency controller through winding I5I.

At the time of starting the oscillator, contact 513 is in engagement with contact I51 since the differential relay BI is not energized. Therefore, when leads I49 and I50 are energized upon closure of switch I15, the buzzer circuit would be energized through the resistance I16, contacts I51 and I56 to ground at HI and thence to the lead I50 through the ground I43. Howe ever, since energization of the buzzer would be undesirable during starting period, switch I10 is provided with a contact I18 which serves the purpose of short circuiting the buzzer winding and allowing all of the current in the filament circuit to flow through the resistance I69. To provide this result, switch I10 has its movable contact I11 coordinated with respect to the movable contact I14 of switch I15 such that contact I11 engages contact I18 at the same time contact I14 engages contact I16. The circuit established upon engagement of contacts I11 and I18 comprises contact I11, lead I01 to resistor '95, thence to ground 96 and from ground 96 to ground Ili through contacts I58 and I51 through lead I66, thence through buzzer winding I61 to the short circuit contact I18. By means of this circuit all of the current is caused to flow through the resistance I69 and the buzzer or signal does not operate.

For practical purposes, it is desirable to allow a momentary period for the tubes to warm up before placing the oscillator into operation, that is, before completing the circuit from B to the filament. Provision of a detent or hold position for the knob III, at which contact I11 is in engagement with contact I18, serves this purpose.

As the control knob III is moved beyond the hold position, contact I11 momentarily sweeps past a stationary contact I19 and at the same time leaves engagement with the contact I16. Contact I 19 is connected to the filament tap lead 63; therefore, the momentary engagement of contacts H1 and I19 completes the circuit between B- and the filament of the oscillator and when the oscillator starts to operate the frequency control circuit is energized which allows the differential relay I3! to assume control of the machine. At this moment, the control contact E58 is moved into engagement with the control contact i56 which breaks the buzzer circuit. Once the contact i53 has engaged contact I56, the circuit between filament and B of the oscillator is. maintained. from the filament tap through lead N33 to lead I62 through the plate control relay winding to the stationary contact 155, then through the contact I58 to the ground at ill and from here to ground which is in connection with the grid of the power tube through resistance 95. When this circuit is completed, the machine is in full operation. Since contact I11 is no longer in engagement with contact i178. the buzzer circuit is not short circuited but is ready to provide a signal should any frequency deviation occur which will allow the differential relay to drop out. Also, since the engagement of contacts ill and 119 was momentary only, the differential relay functions to control the circuit. In event of plate overload independently of any frequency variations, relay as described in United States Patent No. 2,261,153

to Carl K. Gieringer. It also may be noted that while the plate circuits of the triode tubes of the frequency controllers shown in Figures 1 and 3 are connected to the resonant circuits for excitation by the oscillator, the plates of these tubes may be energized from any suitable source such as sixty (60) cycle alternating current or forming independent circuit of higher frequency.

For convenience, in the construction of the apparatus, frequency controllers of the type shown in Figures 1 and 3 may be built as separate units having plugs arranged for engagement with sockets through which the circuit connections may be established to the oscillator.

Having described our invention, we claim:

1. In combination, an oscillator, a switch for disrupting oscillator operation, a differential relay for controlling said switch, a first circuit connected to derive a voltage from the oscillator and including a rectifier connected to energize one winding of said differential relay, and a second circuit connected to energize the other winding of the differential relay, said second circuit including a triode tube, and means for biasing the grid of the tube by a voltage derived from the first circuit, whereby a decrease in the voltage derived from the resonant circuit, attending a variation in frequency from resonance thereof, is manifest as a compound efiect upon the differential relay through an increase in the current flowing in the second circuit.

2. The combination with an oscillator of a frequency monitor responsive to frequency devia-- tions of said oscillator, said monitor comprising; a differential relay, an oscillator control switch responsive to said differential relay, a resonant circuit for energizing one winding of said relay and a relay sensitizing circuit in connection with said resonant circuit and with the other winding of said relay, said relay sensitizing circuit being constructed and arranged to generate in the second winding a flux counteracting the effect of the first flux in respect to energization thereof by said resonant circuit.

3. A frequency controller for an oscillator comprising; an oscillator control switch, a differential relay for actuating said switch, a resonant circuit for deriving a voltage from an oscillator, a rectifier energized from the resonant circuit, a differential relay having one winding connected for energization from said rectifier, said rectifier having a biasing resistor connected therewith, and a triode tube for energizing a second winding of said differential relay in opposition to energization by the first relay, said triode tube having its grid subject to a negative bias by said biasing resistor.

4. The combination with an oscillator of an oscillator control switch, a differential relay for controlling said switch to oil and on positions, a resonant circuit connected to derive a voltage from said oscillator including a rectifier connected to energize one winding of said differential relay, said rectifier having a biasing resistor connected therewith, and a triode tube connected differentially to energize a second winding of said control relay, said triode tube having its grid subject to a negative bias from said biasing resistor and its plate in connection with said resonant circuit.

The combination of an oscillator, a control switch for said oscillator, a differential relay for controlling said switch and having windings for generating opposed fluxes, a triode tube for energizing one of said windings, a rectifier for energizing the other of said windings, said rectifier havin a biasing resistor in connection therewith, means for biasing said triode tube by the current flowing in said biasing resistor, and a resonant circuit connected to derive a voltage from said oscillator for energizing said rectifier.

6. The combination of an oscillator, a control switch for said oscillator, a differential relay for controlling said switch and having windings for generating opposed fluxes, a triode tube for energizing one of said windings, a rectifier for energizing the other of said windings, said rectifier having a biasing resistor in connection therewith, means for biasing said triode tube by the current flowing in said biasing resistor, and a resonant circuit connected to derive a voltage from said oscillator for energizing said rectifier whereby the voltage in said resonant circuit is maximum at a. predetermined resonant frequency, and whereby decrease in voltage from resonant frequency is manifest as a compound effect at said differential relay.

'7. A short wave oscillator including an electronic power tube, an overload relay in connection with the plate circuit of said tube, an oscillator control switch movable to off and on positions, said control switch being responsive to said overload relay in event of excessive plate current conditions in said oscillator, a differential relay also arranged for actuation of said switch in response to variations of predetermined magnitude from a predetermined frequency of operation of said oscillator, and means for energizing said differential relay comprising; a rectifier for energizing one winding of said relay, a resonant circuit connected to derive a voltage from said oscillator for energizing said rectifier, a triode tube arranged differentially to energize a second winding of said relay, and means for furnishing a negative bias to the grid of said triode tube proportional to the current flowing in said rectifier, said differential relay being constructed to hold said oscillator control switch in closed position against the effect of said overload relay while the oscillator is operating within a predetermined range of frequency and to open said switch in event of plate current overload or in the event of frequency deviation of said oscillator beyond a predetermined range.

8. In an oscillator having an electronic power tube, an oscillator control switch and a pair of control relays for actuating said switch, one of said relays being in connection with the plate circuit of said tube for actuating said switch to off position when the plate current exceeds a predetermined value and a frequency responsive device, connected with said oscillator for excitation thereby for actuating said control switch through the second of said relays upon deviation in the frequency of said oscillator beyond a predetermined frequency band.

9. In an oscillator having an electronic power tube, an oscillator control switch and a pair of control relays for actuating said switch, one of said relays being in connection with the plate circuit of said tube for actuating said switch to off position when the plate current exceeds a predetermined value, a frequency responsive device, connected with said oscillator for excitation thereby for actuating said control switch through the second of said relays upon deviation in the frequency of said oscillator beyond a predetermined frequency band, and a signal device in partial circuit connection with said control switch includin a circuit completing contact at said control switch which is engaged upon actuation of said control switch to off position.

10. In an oscillator having a power tube, a rela in connection with the plate circuit of said tube and arranged to be energized when the plate current exceeds a predetermined value, a resonant circuit connected with said oscillator for excitation thereby, a differential relay having one winding in connection with said resonant circuit so as to generate a flux in response to voltages in said resonant circuit, means for producing a counteractive flux in the second winding of the differential relay in response to voltage variations in the resonant circuit coincidental with deviations in frequency of said oscillator beyond the predetermined frequency band, an oscillator control switch responsive to both relays for actuation thereby to off position, an input control switch for said oscillator and means for placing said oscillator in operation independently of the second of said relays.

11. In an oscillator having an electron power tube, a. relay in connection with the plate circuit of said tube and arranged to be energized when the plate current exceeds a predetermined value, a resonant circuit connected with said oscillator for excitation thereby, a differential relay having one winding connected with said resonant circuit to produce a magnetic force in response to voltage variations therein, means in circuit connection with the resonant circuit and the second winding of the differential relay for producing in said second winding a magnetic force counteracting that in the first winding as caused by variations in the voltage of the resonant circuit in response to deviations in frequency of said oscillator beyond the predetermined frequency band, an oscillator control switch responsive to both relays for actuation thereby to off position, an input control switch for said oscillator, and means for placing said oscillator in operation independently of the second of said relays including a device for short circuiting said second relay.

12. In an oscillator having a power tube, an oscillator control switch having off and on positions, means for completing a circuit to the grid of said tube in on position of said switch, a signal device, means for completing a circuit to said signal device in off position of said switch, a relay for holding said switch in on position, a resonant circuit connected with said oscillator for excitation thereby, means for controlling said relay by said resonant circuit whereby said switch is actuated to off position upon deviation in frequency of said oscillator beyond a predetermined frequency band, an input control switch for said oscillator, and means for starting said oscillator independently of said relay.

13. In an oscillator having a power tube, an oscillator control switch having off and on positions, means for completing a, circuit to the grid of said tube in on position of said switch, a signal device, means for completin a circuit to said signal device in off position of said switch, a relay for holding said switch in on position, a resonant circuit connected with said oscillator for excitation thereby, means for controlling said relay by said resonant circuit whereby said switch is actuated to off position upon deviation in frequency of said oscillator beyond a predetermined frequency band, an input control switch for said oscillator, and means for starting said oscillator independently of said relay and means for coordinately short circuiting said signal device until said relay has been energized through said resonant circuit to actuate said switch to on position.

14. The combination, with an oscillator, of an oscillator control switch, a differential relay for controlling said switch, a resonant circuit connected with said oscillator for excitation thereby, means for ener izing one winding of said differential relay from said resonant circuit, and means operated in conjunction with said resonant circuit for inversely energizing the other winding of said differential relay to provide an increased flux effect therein attending deviations in frequency of said oscillator, whereby predetermined sensitivity of said differential relay is maintained independently of oscillator voltage.

15. The combination with an oscillator of an oscillator control switch, a differential relay for controlling said switch, a resonant circuit connected with said oscillator for excitation thereby, means for energizing said one winding of differential relay from said resonant circuit, and means operated in conjunction with said resonant circuit for inversely energizing the other winding of said differential relay to provide an increased flux effect therein attending deviations in frequency of said oscillator whereby predetermined sensitivity of said differential relay is maintained independently of oscillator voltage, and whereby substantially uniform sensitivity of said relay is maintained through a predetermined frequency band.

16. An oscillator circuit having a tank coil, an output coil coupled therewith, a control member for varying the coupling of the output coil with the tank coil, an oscillator control switch, a resonant circuit responsive to oscillator frequency for actuating said control switch upon deviation of oscillator frequency beyond a predetermined frequency band, a signal circuit, means for energizing said signal circuit upon actuation of said oscillator control switch by said frequency monitor, an input control switch for said oscillator, and an oscillator starting switch for momentarily governing said oscillator independently of said oscillator control switch, both of said latter switches being coupled with said control member for actuation in unison therewith.

CARL K. GIERINGER. ARTHUR G. BILLIN.

REFERENCES CITED UNITED STATES PATENTS Name Date Gieringer Nov. 4, 1941 Number 

